1. Field of the Invention
The present invention relates to a webbing retractor for a webbing belt which restrains a vehicle occupant.
2. Description of the Related Art
A locking device is provided at a webbing retractor which forms a main portion of what is known as a seat belt apparatus, which restrains a vehicle occupant by means of an elongated belt-shaped webbing belt. When a vehicle rapidly decelerates, the locking device locks a winding shaft to oppose a force applied by a body of the vehicle occupant, which begins to move toward the front of the vehicle due to inertia in the rapid deceleration state and starts to pull out the webbing belt. In this way, the locking device increases the restraining force of the webbing belt at the time of rapid deceleration of the vehicle.
An example of this type of locking device is briefly described below.
The locking device is provided with one or a plurality of lock plates attached to the winding shaft so as to be displaceable within a predetermined range along a radial direction of the winding shaft. Ratchet teeth are formed at an outer peripheral portion of each of these lock plates. When the lock plates are displaced, with respect to the winding shaft, outward in a radial direction of the winding shaft, the ratchet teeth mesh with ratchet teeth of a ratchet hole formed in one of a pair of leg plates that form a frame of the webbing retractor, thereby locking the winding shaft.
A rotating body is provided in a vicinity of these lock plates so as to be rotatable coaxially with the winding shaft. The rotating body is mechanically coupled to the winding shaft by an urging member such as a compression coil spring, a torsion coil spring, or the like, and rotates along with the winding shaft. When an external force that opposes this rotation with the winding shaft is applied to the rotating body, the urging member deforms elastically and the rotating body rotates relatively to the winding shaft. The rotating body is engaged with the lock plates, and when the rotating body rotates relative to the winding shaft, the lock plates are displaced outward in the radial direction of the winding shaft.
An acceleration sensor is provided at a side of the rotating body. The acceleration sensor is provided with a locking member which locks rotation of the rotating body when the acceleration sensor detects a vehicle deceleration of a predetermined magnitude or more.
When the body of the vehicle occupant pulls out a webbing belt due to inertia at a time of rapid deceleration of the vehicle, the winding shaft rotates in a pulling-out direction (i.e. in a direction in which the webbing belt is pulled out). However, when the acceleration sensor detects such a state of rapid deceleration, the locking member locks rotation of the rotating body, and therefore, relative rotation occurs between the winding shaft and the rotating body. The relative rotation of the rotating body at this time displaces the lock plates outward in the radial direction of the winding shaft. The rotation of the winding shaft is locked by the ratchet teeth of the lock plates meshing with the ratchet teeth of the ratchet hole, and pulling-out of the webbing belt is limited.
In the locking device described above, a compression coil spring may be used as the urging member. In the locking device described above, as well as in other devices, a compression coil spring may be attached by the following method. First, a cylindrical boss having a slightly smaller outside diameter than an inside diameter of the compression coil spring is formed as a projection, from a portion to which one end portion of the compression coil spring abuts, along an axial direction of the compression coil spring (specifically, the axial direction of the compression coil spring when it is regarded from the shape thereof as a cylinder). Then, the compression coil spring is attached to the boss such that the boss is inserted into the compression coil spring. Displacement of the compression coil spring in a direction perpendicular to the axial direction of the boss is limited by the boss.
The above-described method for attaching a compression coil spring is usual. However, it has the following problems when applied to attachment of a compression coil spring in the locking device described above.
In the locking device described above, a disc or the like for limiting displacement of the lock plates and of the winding shaft itself along the axial direction of the winding shaft is integrally provided at the winding shaft at a side of the lock plates opposite to the side at which the rotating body is disposed. Between the disc and the rotating body, the abutting portion and the boss described above are formed and the compression coil spring is disposed. In this case, an opening is provided in the rotating body in advance in order to facilitate attachment of the compression coil spring. The compression coil spring is disposed between the rotating body and the disc through this opening.
In order that the compression coil spring can be attached and that secure attachment can be confirmed, the opening needs to be formed so that one end of the opening in the longitudinal direction thereof is at a position which is almost coplanar with the plane in which the base portion of the boss exists and, further, the length from a position corresponding to a distal end of the boss to the other end portion of the opening in the longitudinal direction thereof is longer than the total length of the compression coil spring when the compression coil spring is fully compressed.
However, providing a boss at each of both longitudinal direction ends of the compression coil spring is fundamentally difficult. Hence, the compression coil spring is only supported by the boss provided at the one longitudinal direction end portion of the compression coil spring. Therefore, the other longitudinal direction end portion of the compression coil spring is extremely unstable, and the compression coil spring can easily come off through the opening having the size described above.
Further, when the compression coil spring is attached to a structure as described above, the compression coil spring cannot pass through the opening unless it is fully compressed in advance. Therefore, it is extremely difficult to automate the attachment process of the compression coil spring.
In view of the aforementioned, an object of the present invention is to provide a webbing retractor which facilitates reliable attachment of a compression coil spring, and from which such an attached compression coil spring does not easily come off.
A first aspect of the present invention is a webbing retractor for connection to an axially rotatable winding shaft having a webbing belt with an end, the end being connected to the winding shaft, which takes-up the webbing belt by rotation in a retracting direction, the webbing belt being for restraining a vehicle occupant, the winding shaft having a locking device with a rotating body coaxially rotatable with the winding shaft in a pulling-out direction, the pulling-out directing being opposite to the retracting direction, the locking device including a locking mechanism preventing rotation of the winding shaft in the pulling-out direction when there is a sudden vehicle deceleration, the webbing retractor including: a pair of wall portions with a first wall portion provided at the rotating body and a second wall portion provided at the winding shaft at a retracting direction side of the first wall portion and faces the first wall portion; a compression coil spring which is disposed between the pair of wall portions, and which is compressed by a pressing force applied from the second wall portion due to rotation of the winding shaft in the pulling-out direction, and which presses the first wall portion by restoring force from the compressed state of the compression coil spring; limiting portions, at least one of which is provided integrally with the rotating body and at least one of which is provided integrally with the winding shaft, and which limit at an outer side of the compression coil spring displacement of the compression coil spring along a direction perpendicular to an axis of the compression coil spring; and an insertion hole provided between the pair of wall portions and penetrating the rotating body at a position further toward the second wall portion than to the first wall portion, and an opening dimension of the insertion hole along a direction from the first wall portion to the second wall portion is larger than a total length of the compression coil spring in a compressed state and smaller than a total length of a natural length of the compression coil spring, and the compression coil spring is inserted through the insertion hole between the pair of wall portions and into a region at an inner side of the limiting portions from a side of the rotating body opposite a side at which the wall portions exist.
In the webbing retractor with the above structure, when the winding shaft rotates in the pulling-out direction in a normal state, the second wall portion provided at the winding shaft begins to compress the compression coil spring by pressing the compression coil spring in the pulling-out direction, and the compression coil spring receiving the pressing force presses the first wall portion provided at the rotating body by an elastic force thereof. Thus, the rotating body rotates in the pulling-out direction, following the rotation of the winding shaft.
When the webbing belt is pulled out and the winding shaft is rotated in the pulling-out direction in a state in which rotation of the rotating body is limited or an external force in the retracting direction is applied to the rotating body, the second wall portion compresses the compression coil spring whereas the first wall portion opposes the elastic force of the compression coil spring. Therefore, the rotating body rotates in the retracting direction relatively to the winding shaft. When the rotating body relatively rotates, the locking mechanism operates to lock rotation of the winding shaft in the pulling-out direction. Thus, the webbing belt cannot be pulled out further in this state.
Since displacement of the compression coil spring in a direction along a direction perpendicular to the axis of the compression coil spring is limited from the outer side of the compression coil spring by limiting portions provided at at least one of the rotating body and the winding shaft, malfunction or the like due to an inadvertent displacement of the compression coil spring in the direction perpendicular to the axis of the compression coil spring is prevented.
Further, since the limiting portions limit displacement of the compression coil spring at the outer side of the compression coil spring, it suffices for the compression coil spring to be inserted between the limiting portions when it is assembled. Therefore, assembly of the compression coil spring is easier than in a conventional structure in which displacement of the compression coil spring is limited by a boss.
Furthermore, in the present webbing retractor, even though the compression coil spring is still assembled by being inserted between the rotating body and the winding shaft through the insertion hole formed in the rotating body, the insertion hole opens at a wall portion other than the wall portion where the limiting portions of the rotating body and the winding shaft are provided, and the length of the insertion hole in a direction along the axial direction of the compression coil spring is long enough for the compression coil spring to be able to pass therethrough in a compressed state. Therefore, the length of the insertion hole in the direction along the axial direction of the compression coil spring can be made smaller than the length thereof in a conventional structure using a boss, and the compression coil spring can be prevented from coming off after assembly.
The webbing retractor of the present invention, preferably further includes a pressing portion provided integrally with the winding shaft at a side of the second wall portion which side is opposite to a side at which the first wall portion exists, the pressing portion pressing the first wall portion toward the retracting direction when the winding shaft rotates in the retracting direction.
In the webbing retractor of the above structure, when the winding shaft rotates in the retracting direction, the second wall portion moves in a direction of moving away from the first wall portion. However, in this case, the pressing portion presses the first wall portion provided at the rotating body side, and the rotating body thereby follows the rotation of the winding shaft in the retracting direction. That is, in the present webbing retractor, since the rotating body is made to follow the rotation of the winding shaft without using the elastic force of the compression coil spring when the winding shaft rotates in the retracting direction, the compression coil spring only need to be disposed between the pair of wall portions. Therefore, an end portion of the compression coil spring does not particularly need to be fixed, and assembly of the compression coil spring is even easier.